I'm sure you didn't mean to leave out Orkney - Skara Brae etc
There are no books on carved stone balls that i know of .Although there are a couple of good PSAS articles ,particularly the one by Dorothy Marshall .I'll dig out the details . They are very localised to Aberdeenshire with just a few strays in Fife , Angus and futher south and west . The Towie ball is incredible and certainly has similarities ,like others with RA .[/quote]